This invention relates to polyblends and specifically to polyblends of ABS polymers with styrene/maleic anhydride copolymers having a rubber modifier incorporated therein.
ABS polymers are formed by the polymerization of styrene and acrylonitrile in the presence of a diene rubber such as polybutadiene. They may be made by mass, suspension or emulsion polymerization techniques. The diene rubber is present as a substrate grafted with a styrene/acrylonitrile superstrate. A styrene/acrylonitrile matrix is usually formed simultaneously with the grafting reaction. Further matrix may be added subsequently in a blending operation to obtain the desired formulation.
Besides the compositions described above, the term "ABS polymer" is often used to cover variations in this formulation through substitution of other copolymerizable monomers, in whole or in part, for one or more of the components of standard ABS. Thus, the acrylonitrile can be wholly or partially substituted for example by methacrylonitrile or wholly substituted by methyl methacrylate; polybutadiene can be replaced with a wide range of other rubbers having a Tg (glass transition temperature) below 0.degree. C. and preferably below -30.degree. C.; and styrene can be replaced by substituted styrene such as halostyrenes, .alpha.-methyl styrene and the like. All such variations are embraced by the term ABS polymer as it is used herein.
The term "ABS" is conventionally used to describe compositions comprising the "styrene" and "acrylonitrile" monomer components in a weight ratio of from 80:20 to 60:40.
ABS polymers are very well known in the field of molding materials as being suitable for the production of tough, moldable materials with good surface properties. ABS is adapted for use in such diverse fields as automotive parts, housings for major appliances such as refrigerators and washing machines, television cabinets, body work for small appliances such as blenders, mixers, pocket calculators, radios, telephones and containers for food-stuffs. The polymers however, have a disadvantage in that they generally have too low a heat distortion temperature for certain uses where the item made from the polymer is expected to operate at a relatively high temperature, without becoming distorted. This disadvantage somewhat limits the range of potential end-uses for which ABS is adapted. The present invention provides a composition based on ABS which has a significantly higher heat distortion temperature than ABS and is therefore capable of performing adequately under higher temperature conditions while retaining much of the toughness that characterizes ABS polymers.